Research from the net indicates the original references mentioned by Ducks Unlimited. The scientific report (2003) from Washington State was reviewed by a Massachusetts report (2012). Links given at bottom. Page numbers refer to the 2012 report.

Clearly there are a lot of unknowns regarding spraying this chemical in the ocean. Large gaps in information are highlighted in the second report. Reading the information in the Appendices was very informative. It highlights details of the risk assessments and limitations. What I didn’t like was the dismissal of “observed information” as if it didn’t count. They must follow the exact guidelines set by someone (FDA?) to be accepted.


Eastern Oyster. MRID 41315802 (Supplemental). In a 96-hour flow-through test,

No mortalities were observed in either the treated or control groups. There was a statistically significant decrease in mean shell deposition

(p. 57

Rainbow Trout. MRID 41315804 (Supplemental). In an early life-stage flow-through test, imazapyr acid resulted in significantly reduced percent hatch and an observed reduction on survival…

(p. 61

Monocots (4 species)(corn, oats, onion, wheat) and Dicots (4 species)(sunflower, cucumber, tomato, sugarbeet) vegetative vigor study —

Only descriptive summary data was presented; consequently effect levels were not determined. Observed effects included chlorosis, stunting, leaf tip burning, necrosis, and plant death.

A second study showed chlorosis, stunting and plant death with full analysis.


123-2 Aquatic Plant Vascular

Imazapyr is considered highly toxic and expected to exert a detrimental effect on vascular aquatic plants (duckweed). The study is scientifically sound and meets guideline protocols. (what about eelgrass?)


Chronic Risk to Estuarine/Marine Fish

Estimated chronic effects for estuarine/marine fish uncertain because no chronic data were submitted by the registrant;…

Chronic Risk to Estuarine/Marine Invertebrates

Estimated chronic effects for estuarine/marine invertebrates uncertain because no chronic data were submitted by the registrant; …

This document bases much of the “risk analysis” on modelling not actual real life testing.

The model results indicate that dissolved imazapyr dissipates in large part within a month following the application and that dissipation of imazapyr is primarily the result of photolysis (Fig. 5.1). (sunlight) – do we get that here?

(p. 19

The application of Habitat and Imazapyr E Pro to post-emergent vegetation requires the addition of an adjuvant to the tank mix. As pointed out in the review for imazapyr use in the San Francisco Estuary (Pless, 2005), adjuvants may greatly increase the toxicity of the herbicide tank mix solution.

(p. 29

But what really stands out is this paragraph:

Application to Waters used for Irrigation Water treated with these products may not be used for irrigation purposes for 120 days after application or until product residue levels are determined by laboratory analysis, or other appropriate means of analysis, to be 1.0 ppb or less.

However, as stated in this document it is ok for people to swim in areas recently sprayed.


This document reviewed the following Washington State Assessment and listed shortcomings of the Washington document.

Washington State Reviews and Risk Assessments Ecological Risk Assessment of the Proposed Use of the Herbicide Imazapyr to Control Invasive Cordgrass (Spartina spp.) in Estuarine Habitat of Washington State. 2003.

Available at: